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According to collision theory, in the modified rate expression Rate = P Z_AB e^(-Ea/RT), what does the steric factor P account for?
AProper orientation of colliding molecules
BTotal number of collisions per second
CFraction of molecules above threshold energy
DThe activation energy of the reaction
Answer & Solution
Correct answer: A. Proper orientation of colliding molecules
1. $Z_{AB}$ is the collision frequency and $e^{-E_a/RT}$ is the fraction of energetic collisions.
2. Not all energetic collisions react; molecules must also be correctly oriented.
3. The steric (probability) factor P accounts for this proper orientation.
4. So option B describes Z and option C describes the exponential term, not P.
_Source: NCERT Class 12 Chemistry Ch 3 "Chemical Kinetics", p.22_
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